Plants produce a vast and diverse assortment of organic compounds, the great majority of which do not appear to participate directly in growth and development. These substances, traditionally referred to as secondary metabolites or plant natural products, often are distributed among limited taxonomic groups within the plant kingdom. The functions of secondary metabolites remain largely unknown, although a number of compounds have been associated with e.g. protection against herbivores and protection against microbial infection, as attractants for pollinators and seed-dispersing animals, and as compounds that influence competition among plant species (allelochemicals).
There is a growing interest in plant natural products, since these products often have a wide range of applications in different kinds of industries, including pharmaceutical industries, cosmetic industries, food industries, detergent industries, etc.
Saponin is an example of a group of plant secondary metabolites. Saponins are glycosylated compounds classified as either triterpenoids, steroids, or steroidal glycoalkaloids. Saponins consist of one or two sugar moieties which are coupled to the aglycon (mono- and bisdesmosides, respectively). Saponins can be hydrolysed to sapogenins and sugar moieties by acid hydrolysis or enzymatic methods. Saponins are water soluble high molecular weight compounds.
Saponins have a wide range of applications. Saponins have the ability of lowering surface tension and the word “saponin” also reflects this as “sapo” is the latin word for soap. Saponins therefore have potential applications in the cosmetic and in the detergent industries. Saponins furthermore have the ability of forming insoluble complexes with cholesterol, which makes some of them suitable for use in the pharmaceutical industry as cholesterol lowering agents. Saponins also have other therapeutical effects. Saponins from chestnut do e.g. possess anti-inflammatory characteristics. Saponins, when injected into the blood stream, are furthermore highly toxic due to their haemolytic properties. Saponins are usually relatively harmless when ingested orally. Steroidal saponins are of great interest owing to their relationship with such compounds as the sex hormones, cortisone, diuretic steroids, vitamin D and cardiac glycosides. Also, saponins are associated with formation of immunostimulating complexes (ISCOMs) (Morein et al., (1995) Clinical Immunotherapeutics 3: 461-475) that are useful in vaccine strategies.
At present however, a major obstacle in exploiting the wide range of potential applications of saponins is the fact that commercially available saponins are relatively expensive.
Commercially available plant extracts containing saponins are e.g. extracts of Saponaria officinalis, Quillaia bark and stem, Castanea sativa seeds, and extracts of various Yucca species. Liquorice root, primula root, and senega root can also serve as raw material for saponin extracts. A problem in this field is that the available sources of saponin extracts are relatively few. And in some cases, e.g. Quillaia bark, the plants are often sparse and expensive because they cannot be cultivated in an efficient manner. Usually the saponins are present in relatively low concentrations. The commercially available saponin extracts are thus often expensive and/or sparse. It should also be noted that the saponins are quite complicated compounds and it has not so far been profitable to develop methods for chemical synthesis of these compounds.
Plant extracts containing saponins and sapogenins are thus of general interest within a wide range of different industries. There is therefore a growing need in the art for alternative sources of saponin extracts and these plant sources should preferably be cheap, easy to obtain, and preferably the saponin content should be relatively high.
For the general description of saponins, extraction, production, and use of saponins reference is made to Ullman's Encyclopedia of Industrial Chemistry (1993), Vol. A23, pp. 485-498. Furthermore, the literature is abundant concerning the extraction, composition and specific effects of the individual saponins derived from plant materials.
The fruits from the butter trees; the African shea tree ((Bassia) Butyrospermum parkii or Vitellaria paradoxa) and Indian butter tree (Bassia latifolia and B. longifolia; or Madhuca Sp.) of the Sapotacea family contain seeds (nuts) that are suitable for extraction and production of butter fat. Shea butter fat and Indian butter fat have a wide range of applications including as food, food ingredient, emulsifier, and also as an ingredient in the production of cosmetics.
Extraction and production of butter fat leaves a press cake or an extracted residue (meal) as a by-product (waste product). It has proven difficult to find normal outlets for this by-product as an ingredient in e.g. animal feed. This is probably due to a content of secondary metabolites that are toxic to mammals. Consequently the material is presently disposed off by e.g. burning.
An investigation of an alcohol extract from “mowrah meal” from the Indian butter tree Bassia latifolia as well as other related species revealed presence of a novel triterpene sapogenin called “bassic acid” (C30H46O5) (Heywood et al., J. Chem. Soc. (1939), Part V, pp. 1124-1129). Bassic acid from B. butryrace was extracted with a solution containing 5% hydrochloric acid. Bassic acid was also identified in the by-product from shea tree. It is disclosed that saponins and sapogenins can be extracted from by-products by water or alcohol extraction. The document does not disclose any methods of stabilising the saponins in the watery solution from undergoing hydrolysis. Likewise, no possible applications of the extracts are disclosed herein and consequently no companies have been encouraged to exploit by-products for production of saponin/sapogenin extracts on basis of this study published in 1939.